Numerical modeling of interspecific competition between filamentous and nonfilamentous periphyton on a flat channel bed

Abstract

Interspecific competition between filamentous and nonfilamentous periphyton usually results in predominance of filamentous periphyton in natural shallow river streams. The mechanisms of this interspecific competition must be known to understand the growth characteristics and primary productivity of stream periphyton communities. In the present study, a numerical simulation model is presented to describe the growth and interspecific competition between filamentous and nonfilamentous periphyton on a flat channel bed, in which the processes of the interspecific competition are an integral part of the modeling of growth strategies. The temporal growth of each kind of periphyton is calculated by balancing primary production, immigration, respiration, and detachment. For the modeling of primary production and respiration, transportation of nutrients and other substances inside the biofilm is estimated using diffusion equations including the effect of turbulent diffusivity near the channel bed surface. In estimating the immigration rate, different immigration functions for filamentous and nonfilamentous periphyton are used in order to represent the different effect of turbulent flow on the immigration strategy of each type of periphyton. A series of numerical computations under different hydraulic conditions shows that the degree of dominance of filamentous periphyton increases with time, and the net primary production of periphyton increases with increasing friction velocity.